perf/arm_dmc620: Add cpumask

Add a cpumask for the DMC620 PMU. As it is an uncore PMU, perf
userspace tool only needs to open a single counter on the CPU
specified by the CPU mask for each event on a given DMC620 device.

Signed-off-by: Xin Yang <xin.yang@arm.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20230613013423.2078397-1-xin.yang@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

drivers/perf/arm_dmc620_pmu.c

@@ -227,9 +227,31 @@ static const struct attribute_group dmc620_pmu_format_attr_group = {
 	.attrs	= dmc620_pmu_formats_attrs,
 };
 
+static ssize_t dmc620_pmu_cpumask_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	struct dmc620_pmu *dmc620_pmu = to_dmc620_pmu(dev_get_drvdata(dev));
+
+	return cpumap_print_to_pagebuf(true, buf,
+				       cpumask_of(dmc620_pmu->irq->cpu));
+}
+
+static struct device_attribute dmc620_pmu_cpumask_attr =
+	__ATTR(cpumask, 0444, dmc620_pmu_cpumask_show, NULL);
+
+static struct attribute *dmc620_pmu_cpumask_attrs[] = {
+	&dmc620_pmu_cpumask_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group dmc620_pmu_cpumask_attr_group = {
+	.attrs = dmc620_pmu_cpumask_attrs,
+};
+
 static const struct attribute_group *dmc620_pmu_attr_groups[] = {
 	&dmc620_pmu_events_attr_group,
 	&dmc620_pmu_format_attr_group,
+	&dmc620_pmu_cpumask_attr_group,
 	NULL,
 };